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United States Patent |
5,103,327
|
Hirai
,   et al.
|
April 7, 1992
|
Active matrix liquid crystal display element and a projection type
active matrix liquid crystal display apparatus
Abstract
An active matrix liquid crystal display element comprises an active matrix
substrate having an active element for each electrode for picture element,
a counter electrode substrate provided with a counter electrode and a
liquid crystal polymer composite material in which a nematic liquid
crystal having a positive dielectric anisotropy is dispersed and held in a
polymer matrix, said liquid crystal polymer composite material being held
between the active matrix substrate and a counter electrode substrate, and
the refractive index of the polymer matrix substantially agreeing with the
ordinary refractive index (n.sub.0) of the liquid crystal used, wherein
the refractive index anisotropy .DELTA.n of the nematic liquid crystal
used is 0.18 or higher, and the average particle diameter R(.mu.m) of the
liquid crystal dispersed and held in the polymer matrix, and the specific
dielectric anisotropy .DELTA..epsilon., the elastic constant
K33(10.sup.-12 N) and the viscosity (cSt) of the liquid crystal satisfy
the following relations:
.DELTA.n.sup.2 .DELTA..epsilon./(K33.multidot..eta.)>0.0011(1)
and
5(K33/.eta.).sup.0.5 >R>(K33/.DELTA..epsilon.).sup.0.05 (2)
Inventors:
|
Hirai; Yoshinori (Yokohama, JP);
Gunjima; Tomoki (Yokohama, JP);
Niiyama; Satoshi (Yokohama, JP);
Kumai; Hiroshi (Yokohama, JP)
|
Assignee:
|
Asahi Glass Company Ltd. (Tokyo, JP)
|
Appl. No.:
|
736382 |
Filed:
|
July 26, 1991 |
Foreign Application Priority Data
| Jul 26, 1990[JP] | 2-196070 |
| Aug 21, 1990[JP] | 2-218224 |
Current U.S. Class: |
349/10; 349/35; 349/86; 349/93; 349/177 |
Intern'l Class: |
G02F 001/133 |
Field of Search: |
350/334,347 V,347 E,350 R
|
References Cited
U.S. Patent Documents
4435047 | Mar., 1984 | Fergason | 350/334.
|
4556289 | Dec., 1985 | Fergason | 350/347.
|
4596445 | Jun., 1986 | Fergason | 350/334.
|
4613207 | Sep., 1986 | Fergason | 350/331.
|
4616903 | Oct., 1986 | Fergason | 350/334.
|
4684220 | Apr., 1987 | Shionozaki et al. | 350/350.
|
4707080 | Nov., 1987 | Fergason | 350/334.
|
4780240 | Oct., 1988 | Emoto et al. | 350/350.
|
4795579 | Jan., 1989 | Vauchier et al. | 350/350.
|
4815825 | Mar., 1989 | Nakagomi et al. | 350/350.
|
4818070 | Apr., 1989 | Gunjima et al. | 350/334.
|
4818428 | Apr., 1989 | Scheuble et al. | 350/350.
|
4834509 | May., 1989 | Gunjima et al. | 350/347.
|
4849130 | Jul., 1989 | Dabrowski et al. | 350/350.
|
4874543 | Oct., 1989 | Yoshida | 350/350.
|
4890902 | Jan., 1990 | Doane et al. | 350/347.
|
4938568 | Jul., 1990 | Margerum et al. | 350/347.
|
4944577 | Jul., 1990 | Yoshida et al. | 350/350.
|
4974940 | Dec., 1990 | Asano | 350/347.
|
4994204 | Feb., 1991 | Doane et al. | 350/334.
|
5004323 | Apr., 1991 | West | 350/334.
|
Primary Examiner: Miller; Stanley D.
Assistant Examiner: Pellman Gross; Anita
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt
Parent Case Text
The present invention relates to an active matrix liquid crystal display
element having an active element for each picture element electrode and a
projection type active matrix liquid crystal display apparatus.
In recent years, liquid crystal displays have been widely used for personal
word processors, hand-held computers, portable TV sets and so on, taking
the advantages of low power consumption, low driving voltage and so on. Of
the liquid crystal displays, active matrix liquid crystal display elements
having an active element for each picture element electrode have
particularly been noted and developed.
As such liquid crystal display elements, there was a proposal on liquid
crystal display elements in which a dynamic scattering mode (DSM) liquid
crystal is used. However, the liquid crystal display element of this type
had a disadvantage of large current consumption because a high value of
electric current passed in the DSM liquid crystal. Now, liquid crystal
display elements in which a twist nematic (TN) type liquid crystal is used
have been widely used. For instance, portable TVs have been widely
commercialized. Since the TN type liquid crystal display element has a
very small leak current and a small power consumption, it is suitable for
using a battery as a power source.
When the active matrix liquid crystal display element is used for DS mode,
the leak current of the liquid crystal itself is large. Accordingly, it
was necessary to provide a large storage capacitance in parallel to each
picture element, and the power consumption of the liquid crystal display
element itself is large.
In the TN mode, since a leak current in the liquid crystal itself is very
small, it is unnecessary to provide a large storage capacitance and the
power consumption of the liquid crystal display element itself can be
small.
In the TN mode liquid crystal, however, there is problem that the
transmittance of light is small because two polarization plates are
required. In particular, when a color filter is used for obtaining a
colored display, only several percents of incident light can be utilized.
It is, therefore, necessary to use a strong light source, as a result of
increasing power consumption.
Further, the TN mode liquid crystal display element has disadvantages of
requiring a very strong light source for projecting a picture image on a
projection screen, difficulty in obtaining a high contrast on the
projection screen, and adverse effect to the liquid crystal display
element due to heat from the light source.
In order to solve the problems in the TN mode liquid crystal display
element, there is proposed such mode that a liquid crystal polymer
composite material in which a nematic liquid crystal is dispersed and held
in a polymer matrix is used, and a low voltage such as 10 V or lower is
sufficient to drive it by utilizing the scattering-transparent
characteristics.
However, for a gray scale display, the response characteristic was poor
particularly in a low voltage region (a dark image area) and a residual
image was easily took place.
Further, when was is necessary to obtain a colored display by using a
plurality of the active matrix liquid crystal display elements each having
the same construction, the chromatic balance in the colored display was
insufficient, and a specified color became conspicuous because the
transmission characteristics are different among colors. Thus, there was a
problem that it was difficult to obtain a clear color display.
The present invention is to eliminate disadvantages of the conventional
liquid crystal display element and conventional projection type active
matrix liquid crystal display apparatus.
As an aspect of the present invention, there is provided an active matrix
liquid crystal display element comprising an active matrix substrate
having an active element for each electrode for picture element, a counter
electrode substrate provided with a counter electrode and a liquid crystal
polymer composite material in which a nematic liquid crystal having a
positive dielectric anisotropy is dispersed and held in a polymer matrix,
said liquid crystal polymer composite material being held between the
active matrix substrate and a counter electrode substrate wherein the
refractive index of the polymer matrix substantially agrees with the
ordinary refractive index (n.sub.0) of the liquid crystal used,
characterized in that the refractive index anisotropy of the nematic
liquid crystal used is 0.18 or higher, and the average particle diameter
R(.mu.m) of the liquid crystal dispersed and held in the polymer matrix,
and the specific dielectric anisotropy .DELTA..epsilon., the elastic
constant K33(10.sup.-12 N) and the viscosity (cSt) of the liquid crystal
satisfy the following relations:
.DELTA.n.sup.2 .multidot..DELTA..epsilon./(K33.multidot..eta.)>0.0011 (1)
and
5(K33/.eta.).sup.0.5 >R>(K33/.DELTA..epsilon.).sup.0.5 ( 2)
As another perspect of the present invention, there is provided a
projection type active matrix liquid crystal display apparatus comprising
a plurality of color light sources, a plurality of active matrix liquid
crystal display elements for receiving light from each of the color light
sources and a projection optical system which synthesizes and projects
light emitted from the active matrix liquid crystal display elements,
characterized in that each of the active matrix liquid crystal display
elements comprises an active matrix substrate having an active element for
each electrode for picture element, a counter electrode substrate provided
with a counter electrode and a liquid crystal polymer composite material
in which a nematic liquid crystal having a positive dielectric anisotropy
is dispersed and held in a polymer material, said liquid crystal polymer
composite material being held between the active matrix substrate and a
counter electrode substrate provided with the counter electrode, and the
refractive index of the polymer matrix substantially agrees with the
ordinary refractive index (n.sub.0) of the liquid crystal liquid used, and
that the average particle diameter R.sub.x (.mu.m) of the liquid crystal
corresponding to each color, which is dispersed and held in the polymer
matrix, the gap d.sub.x (.mu.m) between the counter electrode and the
picture element electrode, the specific dielectric anisotropy
.DELTA..epsilon..sub.x, the elastic constant K33.sub.x (10.sup.-12 N), the
viscosity .eta..sub.x (cSt), and the refractive anisotropy .DELTA.n.sub.x
of the liquid crystal and the main wavelength .lambda..sub.x (.mu.m) of
each of the colors satisfy the following equations:
.DELTA.n.sub.x.sup.2 .multidot..DELTA..epsilon..sub.x /(K33.sub.x
.multidot..eta..sub.x)>0.0011 (1A)
and
5(K33.sub.x /.eta..sub.x).sup.0.5 >R.sub.x >(K33.sub.x
/.DELTA..epsilon..sub.x).sup.0.5 ( 2A)
wherein at least a pair of the active matrix liquid crystal display
elements satisfies the relations:
.DELTA.n.sub.i .multidot.R.sub.i /.lambda.i.apprxeq..DELTA.n.sub.j
.multidot.R.sub.j /.lambda..sub.j ( 6)
and
d.sub.i /R.sub.i .apprxeq.d.sub.j /R.sub.j ( 7)
where i.noteq.j, or it satisfies the relation:
.DELTA.n.sub.i .multidot.d.sub.i.sup.2 /.lambda.i.apprxeq..DELTA.n.sub.j
.multidot.d.sub.j.sup.2 /.lambda..sub.j ( 8)
where i.noteq.j.
As another aspect of the present invention there is provided an active
matrix liquid crystal display element comprising R, G and B color filters,
an active matrix substrate having an active element for each picture
element electrode, a counter electrode substrate provided with a counter
electrode and a liquid crystal polymer composite material in which a
nematic liquid crystal having a positive dielectric anisotropy is
dispersed and held in a polymer matrix wherein the refractive index of the
polymer matrix substantially agrees with the ordinary refractive index
(n.sub.0) of the liquid crystal used, said liquid crystal being held
between the active matrix substrate and the counter electrode substrate,
characterized in that the average particle diameter R (.mu.m) of the
liquid crystal dispersed and held in the polymer matrix, the specific
dielectric anisotropy .DELTA..epsilon., the elastic constant
K33(10.sup.-12 N), the viscosity .eta.(cSt) and the refractive index
anisotropy .DELTA.n of the liquid crystal and the main wavelength
.lambda..sub.x (.mu.m) of each color satisfy the relations:
.DELTA.n.sup.2 .multidot..DELTA..epsilon./(K33.multidot..eta.)>0.0011 (1)
and
5(K33/.eta.).sup.0.5 >R.ltoreq.(K33/.DELTA..epsilon.).sup.0.5 ( 2)
and that at least two colors among the R, G and B colors satisfy the
relation:
d.sub.i.sup.2 /.lambda..sub.i =d.sub.j.sup.2 /.lambda..sub.j ( 8B)
where i.apprxeq.j.
In the active matrix liquid crystal display element of the present
invention, since a liquid crystal polymer composite material capable of
electrically controlling a light scattering state and a light transmission
state is used as a liquid crystal material which is interposed between the
active matrix substrate and the counter electrode substrate, is used,
polarization plates are no more necessary, and the transmittance of light
at the time of transmission can be greatly improved. Accordingly, a bright
display is possible. In particular, when the active matrix liquid crystal
display element of the present invention is used for a projection type
display apparatus, a projected image having brightness and a high contrast
ratio is obtainable.
Further, since the average particle diameter R.sub.x (.mu.m) of the liquid
crystal in the liquid crystal polymer composite material and the gap
d.sub.x (.mu.m) between the counter electrode and the picture element
electrodes are determined for each hue, a display having good chromatic
balance, a high contrast ratio and brightness can be obtained when the
colors are mixed in a projection type display.
Further, since orientation treatment indispensable for the TN type liquid
crystal display element is not necessary and problems such as the
destruction of the active elements caused by the static electricity
generated upon treatment can also be avoided, production yield of the
liquid crystal display element can be improved remarkably.
Furthermore, since the liquid crystal polymer composite material is in a
state of film after curing, it can reduce such problems as
short-circuiting between the substrates due to the pressure applied
thereto and the destruction of the active elements caused by the movement
of the spacers.
Further, since the specific resistivity of the liquid crystal polymer
composite material is same as that of the TN mode, it is not necessary to
dispose a large storage capacitance on each picture element as in the case
of the DSM, so that the design for the active element is easy and the
electric power consumption by the liquid crystal display element can be
kept low. Accordingly, since the material can be produced by merely
eliminating the step of forming an oriented film from the production steps
for the conventional TN mode crystal display element, the production is
easy.
The specific resistivity of the liquid crystal polymer composite material
is, preferably, not less than 5.times.10.sup.9 .OMEGA. cm, and more
preferably, not less than 10.sup.10 .OMEGA. cm in order to minimize the
voltage drop due to leak current etc., in which there is no requirement
for providing a large storage capacitance on each of the picture element
electrodes.
As the active element, there may be used, for example, a transistor, a
diode, non-linear resistor element, and two or more of active elements may
be disposed to one picture element if necessary. The liquid crystal
polymer composite material is put between an active matrix substrate which
is provided with active element and a picture element electrode connected
therewith and a counter electrode substrate provided with a counter
electrode to thereby constitute a liquid crystal display element.
The liquid crystal display element of the present invention can be used not
only as a direct view type display element but also a projection type
display element. When the liquid crystal display element of the present
invention is used as the direct view type display element, a display
apparatus may be constituted in combination with a backlight, a lens, a
prism, a mirror, a diffusion plate, a light absorbing material, a color
filter and so on in accordance with the display characteristics which are
desired to obtain.
The liquid crystal display element of the present invention is, in
particular, suitable for a projection type display apparatus, and the
projection type liquid crystal display apparatus can be constituted by
combining the liquid crystal display element with a projection light
source, a projection optical system and so on.
In the projection type active matrix liquid crystal display apparatus of
the present invention, when a multi-color display is to be obtained, a
plurality of color light sources and a projection optical system are used.
A conventional projection light source and a conventional projection
optical system such as a lens may be used for the color light source and
the projection optical system. Generally, a plurality of the liquid
crystal display elements are arranged in correspondence to each color
light source so that an image is projected on a screen by synthesizing
colored lights through the liquid crystal display elements.
The color light source may be a plurality of light sources which are used
for different colors, or light from a single light source may be subjected
to color splitting in order to use a single color light. The light emitted
from the color light source is received in the liquid crystal display
element. In the present invention, a plurality of active matrix liquid
crystal display elements are used wherein the characteristics of each of
the display elements are adjusted for each of color light sources. The
lights emitted from the active matrix liquid crystal display elements are
mixed and projected, whereby a bright projection image having good
chromatic balance and a high contrast ratio is obtainable.
In the present invention, a liquid crystal polymer composite material
comprising a polymer matrix having a large number of fine holes and a
nematic liquid crystal having a positive dielectric anisotropy filed in
the fine holes. The liquid crystal polymer composite material is
preferably such one that the refractive index of the polymer matrix
substantially agrees with the ordinary refractive index (n.sub.0) of the
liquid crystal used, and the refractive index anisotropy .DELTA.n of the
liquid crystal used is 0.18 or more. The liquid crystal polymer composite
material is put between the active matrix substrate and the counter
electrode substrate to thereby constitute the liquid crystal display
element. When a voltage is applied across the electrodes of the liquid
crystal display element, the refractive index of the liquid crystal is
changed, and the relation between the refractive index of the polymer
matrix and the refractive index of the liquid crystal is changed. Namely,
when the refractive indices of the both members are in agreement with each
other, a state of transmission is provided, and when not, a state of
scattering is provided.
The liquid crystal polymer composite material comprising the polymer matrix
having a large number of fine holes and the liquid crystal filled in the
fine holes has such a structure that the liquid crystal is sealed in
vacuoles such as microcapsules wherein the individual microcapsules may
not be completely independent or the individual vacuoles may be
communicated with each other through fine gaps like a porous material.
The liquid crystal polymer composite material used for the liquid crystal
display element according to the present invention can be prepared by
mixing a nematic liquid crystal and a material for forming the polymer
matrix into a solution or a latex, by curing the solution or latex by the
application of light or heat, or by removing solvent or by subjection it
to reactive curing thereby separating the polymer matrix and dispersing
the liquid crystal into the polymer matrix.
Use of the photo-curable or heat-curable type polymer is preferred since it
can be cured in an enclosed system.
In particular, use of a photo-curable type polymer is preferred since it
can be cured in a short period of time with little influence of heat.
As a specific production method, the cell may be formed by using a sealing
material, uncured mixture of the nematic liquid crystal and the curable
compound is injected from the injection port in the same manner as in the
conventional nematic liquid crystal display element, and after sealing the
injection port, they can be cured by light irradiation or heating.
The liquid crystal display element according to the present invention may
also be prepared without using a sealing material, for example, by
supplying an uncured mixture of the nematic liquid crystal and the curable
compound on a substrate provided with a transparent electrode as a counter
electrode, overlaying, on that substrate, an active matrix substrate
having an active element for each picture element electrode and then
curing the material by means of light-irradiation or the like.
The periphery of the display element assembly may be sealed by coating the
sealing material. According to this production method, since it is only
required to supply the uncured mixture of the nematic liquid crystal and
the curable compound by means of coating such as roll coating, spin
coating, printing or by the method of using a dispenser or the like, the
injection step is simple and the productivity is extremely high.
Further, the uncured mixture of the nematic liquid crystal and the curable
compound may be incorporated with spacers for controlling the
inter-substrate gap such as ceramic particles, plastic particles or glass
fibers, pigments, dyes, viscosity controllers or any other additives which
does not adversely influence to the performance of the liquid crystal
display element of the present invention.
During the curing step of the liquid crystal display element of the present
invention, if the element is cured under the condition that a sufficiently
high voltage is applied to only a specified portion, it is possible to
render that portion to be a state of normally light transmittance.
Accordingly, when a fixed display is desired, such normally light
transmittance portion may be formed.
In the liquid crystal display element using the liquid crystal polymer
composite material, higher transmittance in the light transmission state
is preferable and the haze value in the light scattering state is
preferably not less than 80%.
In the present invention, the refractive index of the polymer matrix (after
curing) agrees with the ordinary refractive index (n.sub.0) of the liquid
crystal used, in a state of applying voltage.
Thus, light is transmitted when the refractive index of the polymer matrix
agrees with the refractive index of the liquid crystal, while the light is
scattered (opaque) when they do not agree with each other. The scattering
property of the element is higher than that of the liquid crystal display
element in the conventional DS mode and a display having a high contrast
ratio can be obtained.
The object of the present invention is to provide the optimum structure of
the active matrix liquid crystal display element itself which holds the
liquid crystal polymer composite material and the projection type active
matrix liquid crystal display apparatus using such element.
Namely, the active matrix liquid crystal display element wherein it
provides a quick response in a gray scale display while it has good
chromatic balance, a high transmittance at the time of transmission,
exhibits high scattering property (light-shielding property) at the time
of scattering, brightness and a high contrast ratio, and there is no
residual image.
As factors for determining the electro-optical characteristics of the
active matrix liquid crystal display element using the liquid crystal
polymer composite material, there are the refractive index (ordinary
refractive index n.sub.0, extraordinary refractive index n.sub.e), the
specific dielectric coefficient (.epsilon.//, .alpha..perp., where // and
.perp. respectively represent parallel and vertical to the axis of liquid
crystal molecules), the viscosity .eta. and the elastic constant K33 of
the liquid crystal used, the refractive index n.sub.p, the specific
dielectric coefficient .epsilon..sub.p and the elastic constant of the
polymer used, the average particle diameter R and the volume fraction
.PHI. of the liquid crystal dispersed and held in the polymer matrix, the
gap d between the both electrode substrates (the thickness of the liquid
crystal polymer composite material), the maximum effective voltage V
applied to the liquid crystal polymer composite material at the picture
element portions by the active elements, etc.
In the specification, the diameter of the average particle diameter R of
the liquid crystal means the maximum diameter of the particles when the
liquid crystal comprises independent particles or particles which are
partially communicated with each other. On the other hand, the diameter
means the maximum diameter of a region where the orientation of the
directors of the liquid crystal has mutual co-relation when the liquid
crystal assumes a structure in which the major part has mutual
communication.
It is preferable that the liquid crystal dispersed and held in the polymer
matrix consists of independent particles or particles having partial
communication because high scattering performance and high transmittance
performance, when the liquid crystal is drived at a low voltage, can be
effectively obtained without inconsistency. A scattering phenomenon takes
place at the boundary surface of the liquid crystal and the polymer.
Accordingly, the scattering performance is improved as the surface area of
the boundary surface is large. In order to increase the surface area of
the boundary surface with the optimum particle diameter of the liquid
crystal, an amount of liquid crystal should be increased independent of
and separate from the polymer. Namely, it is important to increase the
density of liquid crystal particles. However, when the amount of liquid
crystal is increased separate from the polymer, a phenomenon of liquid
crystal particles being connected with each other is found, and finally
the liquid crystal assumes a structure in which the entire part of the
particles is connected. This results in the missing of the boundary
surface of the liquid crystal separated from the polymer thereby reducing
the scattering property.
Further, it is important for individual particles of the liquid crystal
held in the polymer matrix to have the substantially same driving electric
field in order to reduce the driving voltage. For this, it is advantageous
that there is a clear interface between the liquid crystal and the
polymer. The missing of the interface results in the dispersion of the
driving electric field to thereby apt to reduce the contrast ratio and the
increase of the driving voltage. Accordingly, the liquid crystal particles
dispersed and held in the polymer are preferably independent particles
which exist at a high density, or particles having partial communication.
The electro-optical characteristics for the active matrix liquid crystal
display element using the liquid crystal polymer composite material
according to the present invention is desirable to have high scattering
property when no electric field is applied and to have high transmittance
when an electric field is applied. Namely, it should have a high contrast
ratio in displaying. When a projection type display is carried out by
using such liquid crystal display element, a display of high brightness
and high contrast ratio is obtainable.
In order to obtain the above-mentioned display, it is necessary that the
above-mentioned factors have the optimum relations.
As particularly important factors for determining the electro-optical
characteristics of the active matrix liquid crystal display element among
the above-mentioned factors, there are the refractive index of the liquid
crystal used (refractive index anisotropy .DELTA.n=extraordinary
refractive index n.sub.e -ordinary refractive index n.sub.0), the specific
dielectric anisotropy .DELTA..epsilon., the viscosity .eta., the elastic
constant K33 the average particle diameter R and the distribution of
particle diameter of the liquid crystal, and the gap d between the both
electrode substrates. When the optimum multicolored display is desired,
the average particle diameter R of the liquid crystal and the gap d.sub.x
of between the electrode substrates are determined for each of the liquid
crystal display elements in correspondence to the wave length
.lambda..sub.x of the predominant wave of the color light sources.
The refractive index anisotropy .DELTA.n (=n.sub.e -n.sub.0) of the liquid
crystal used contributes the scattering property when there is no electric
field. Accordingly, it is preferable that the value of the refractive
index anisotropy should be larger in order to obtain high scattering
property. Specifically, it is preferable to be .DELTA.n>0.18, especially,
.DELTA.n>0.22. Further, the ordinary refractive index n.sub.0 of the
liquid crystal used preferably substantially agrees with the refractive
index np of the polymer matrix. In this case, high transmittance property
can be obtained when an electric field is applied. Specifically, it is
preferable to satisfy the relation of n.sub.0 -0.03<n.sub.p <n.sub.0
+0.05. The most important object of the present invention is to obtain the
active matrix liquid crystal display element using the liquid crystal
polymer composite material which exhibits quick response in a case of a
gray scale display and has good chromatic balance.
When the liquid crystal polymer composite material is drived in a static
state, it is drived either in an OFF state or an ON state having a
sufficiently high voltage (not less than the saturated voltage).
Accordingly, the liquid crystal polymer composite material has a response
time less than several tens msec, and therefore, it is generally suitable
for a high speed display. However, a voltage lower than the saturated
voltage can also be used in a gray scale display in order to obtain a half
tone display. In this case, the response time is slower than that at the
driving in the static state. The response time in the gray scale display
apt to be slower than the display with use of a low voltage (dark display)
in particular, the change from the OFF state to a state of low
transmittance is slowest, and the response time in this condition is more
than several tens times as slow as the response time at the static
driving.
The average particle diameter R of the liquid crystal dispersed and held in
the polymer matrix is a very important factor, which contributes the
scattering property when no electric field is applied and the operation of
the liquid crystal when an electric field is applied.
As important factors for determining the response in the gray scale
display, there are the average particle diameter R and the shape of the
liquid crystal held in the polymer, the specific dielectric anisotropy
.DELTA..epsilon., the elastic constant K33 (10.sup.-12 N) and the
viscosity .eta. (cSt) of the liquid crystal used, etc.
A display without any residual image can be obtained in the gray scale
display in a case that single kind of liquid crystal is used, i.e. a
mono-color display is desired to obtained, or a multi-color display is to
be obtained with use of a single element when the following relations are
satisfied:
.DELTA.n.sup.2 .multidot..DELTA..epsilon./(K33.multidot..eta.)>0.0011 (1)
and
5(K33/.eta.).sup.0.5 >R>(K33/.DELTA..epsilon.).sup.0.5 ( 2)
where the average particle diameter R (.mu.m) of the liquid crystal
dispersed and held in the polymer matrix and the specific dielectric
anisotropy .DELTA..epsilon., the viscosity .eta. (cSt) and dielastic
constant K33(10.sup.-12 N) of the liquid crystal are given.
Further, the display without any residual image can also be obtained in the
gray scale display in a case that a plurality of elements and a plurality
kinds of liquid crystal are used when each color satisfies the following
relations:
.DELTA.n.sub.x.sup.2 .multidot..DELTA..epsilon..sub.x /(K33.sub.x
.multidot..eta..sub.x)>0.0011 (1A)
and
5(K33.sub.x /.eta..sub.x).sup.0.5 >R.sub.x >(K33.sub.x
/.DELTA..epsilon..sub.x).sup.0.5 ( 2A)
where R, .DELTA..epsilon., .eta. and K33 are defined above.
In the above-mentioned ranges a torque acting on the liquid crystal at each
voltage in the gray scale display is balanced whereby the display without
residual image can be obtained, and the electric field needed to drive the
liquid crystal can be suppressed to be low. The above mentioned physical
values of the liquid crystal are values in terms of room temperature.
The average vertical diameter R of the liquid crystal dispersed and held in
the polymer matrix depends largely on response time. When the value R
becomes large, the speed of response becomes suddenly low. On the other
hand, when the value R becomes small, the speed of response becomes high
while the electric field needed for driving becomes high.
The optimum range of the value R is determined depending on the
electrostatic energy and the elastic energy of the liquid crystal, and the
balance of the torque acting on the liquid crystal. The upper limit of the
value R and the lower limit of it are respectively 5(K33/.eta.).sup.0.5
and (K33/.DELTA..epsilon.).sup.0.5 in order to obtain the response
characteristics without causing a trouble in display. Especially, it is
preferable that the upper limit of the value R is 4(K33/.eta.).sup.0.5.
Namely, it is preferable that the above-mentioned equations (2) and (2A)
are respectively expressed as the equations (2B) and (2C) described below:
4(K33/.eta.).sup.0.5 >R>(K33/.DELTA..eta.).sup.0.5 ( 2B)
and
4(K33.sub.x /.eta..sub.x).sup.0.5 >R.sub.x >(K33.sub.x
/.DELTA..epsilon..sub.x).sup.0.5 ( 2C)
The elastic constant of the liquid crystal determines an elastic energy to
be accumulated in the liquid crystal. A bend energy derived from the
elastic constant K33 particularly greatly functions in the liquid crystal
polymer composite material, and the bend energy deeply concerns with the
response characteristics and the driving characteristics, i.e. the elastic
torque acting on the liquid crystal. The specific dielectric anisotropy is
concerned with the electric torque acting on the liquid crystal, i.e. the
electric field needed for driving. The viscosity of the liquid crystal
concerns with a viscous torque acting on the liquid crystal. The
above-mentioned equations have the optimally balanced torques. In this
range, response characteristics suitable for displaying moving pictures in
the gray scale display can be obtained with use of a relatively low
electric field. When a projection type active matrix liquid crystal
display apparatus in which a plurality of color light sources and a
plurality of active matrix liquid crystal display elements are used and
picture images produced from the plural active matrix liquid crystal
display elements are synthesized and projected, is used, it is necessary
that each of the active matrix liquid crystal display elements satisfies
the equation (1A) in order that the display elements can be drived by the
application of a relatively low electric field without causing a residual
image in the half tone. Especially, it is preferable that the value of
each of the equation (1) or (1A) is not less than 0.0014. Namely, the
equation ( 1) or (1A) is preferably expressed as the equation (1B) or (1C)
respectively:
.DELTA.n.sup.2 .multidot..DELTA..epsilon./(K33.multidot..eta.)>0.0014 (1B)
or
.DELTA.n.sub.x.sup.2 .multidot..DELTA..epsilon..sub.x /(K33.sub.x
.multidot.N.sub.x)>0.0014 (1C)
Further, it is important that the refractive anisotropy .DELTA.n.sub.x, the
specific dielectric anisotropy .DELTA..epsilon..sub.x, the bend elastic
constant K33.sub.x (10.sup.-12 N), the viscosity .eta..sub.x (cSt) and the
average particle diameter R.sub.x (.mu.m) of the liquid crystal in each
display elements satisfy the equation as follows:
5(K33.sub.x /.eta..sub.x).sup.0.5 >R.sub.x >(K33.sub.x
/.DELTA..epsilon..sub.x).sup.0.5 ( 2)
The average particle diameter R of the liquid crystal dispersed and held in
the polymer matrix is a very important factor which contributes the
scattering property when no electric field is formed and the operating
characteristics of the liquid crystal when an electric field is applied.
Although the scattering characteristics of the liquid crystal when no
electric field is applied is changed depending on the relations of the
refractive index anisotropy .DELTA.n of the liquid crystal used, the
wavelength .lambda. of light and the average particle diameter R of the
liquid crystal, the most effective scattering property of the liquid
crystal per unit quantity of operable liquid crystal provided that
.lambda. is in a visible light region can be obtained when the average
particle diameter R (.mu.m) satisfies the equation:
0.2<R.multidot..DELTA.n<0.7 (3)
In this range, the scattering property exhibits less wavelength dependency,
and a strong scattering state is obtainable over the visible light region,
whereby a display having high contrast ratio can be obtained.
In a case of multi-color display, the following equation should be
satisfied on the active matrix liquid crystal display element for each
color:
0.2<R.sub.x .multidot..DELTA.n.sub.x <0.7 (3A)
Although the response speed becomes high if the average particle diameter
R.sub.x of the liquid crystal display element assumes a value smaller than
the value in the range as described in the equation (3) or (3A), the
scattering property per unit quantity of operable liquid crystal will
decrease, and the electric field necessary for driving the element becomes
high. On the contrary, although it is possible to drive the liquid crystal
display element with a low electric field if the average particle diameter
R.sub.x is greater than the value in the range described in the equation
(3) or (3A), the scattering property per unit quantity of operable liquid
crystal will decrease, and the response speed becomes low.
It is preferable that the particle diameter of the liquid crystal is
uniform. If there is a distribution in the particle diameter, larger
liquid crystal particles reduce the scattering property and smaller liquid
crystal particles raises the density of electric field for driving, with
the result of inviting the raise of driving voltage and the reduction of
contrast. The dispersion .sigma. of the particle diameter is preferably
not less than 0.25 times as the average particle diameter, more
preferably, not less than 0.15 times. The above-mentioned average particle
diameter and dispersion are respectively volume-weighed values.
The gap d (.mu.m) between the electrodes is also important in order to
obtain a sufficient contrast. The gap d (.mu.m) should have a value which
satisfies the following equation:
3R<d<9R (4)
where R (.mu.m) is the average particle diameter of the liquid crystal.
In a case of the multi-color display, the gap d.sub.x (.mu.m) between the
electrodes is also an important factor for the active matrix liquid
crystal display element for each color. The gap d.sub.x (.mu.m) should
have a value in a range which satisfies the equation:
3R.sub.x <d.sub.x <9R.sub.x ( 4A)
where R.sub.x (.mu.m) is the average particle diameter of the liquid
crystal.
In a case that a plurality of color is provided in a single cell, only one
kind of liquid crystal is generally allowed. Accordingly, it is preferable
that the liquid crystal satisfies the following relations:
.DELTA.n.sup.2 .multidot..DELTA..epsilon./(K33.multidot..eta.)>0.0011 (1)
5(K33/.eta.).sup.0.5 >R>(K33/.DELTA..epsilon.).sup.0.5 ( 2)
and
0.2<R.multidot..DELTA.n<0.7 (3)
In a case that three colors R, G and B are provided, since the color of an
intermediate region is green, the following relation should be satisfied:
3R<d.sub.G <9R (4B)
When the three colors R, G and B are used, and the average particle
diameter R.sub.G of the liquid crystal display element corresponding to a
green light source has a value smaller than that as in the range of the
equation (3), there is the wavelength dependency that the scattering
property is stronger at the short wavelength side. Further, since a high
electric field is needed in the operation of the liquid crystal, the
problem of large consumption power arises. On the other hand, the average
particle diameter R.sub.G is larger than a value in the range as in the
equation (3), the wavelength dependency of the scattering property becomes
small. However, there arise problems that the scattering property becomes
weak over the entire visible light region, the contrast ratio decreases,
and the response in the transition time from a transmission state to a
scattering state becomes slow. Accordingly, the above-mentioned range is
most preferable. In this case, the gap d.sub.G between the electrode
substrates of the liquid crystal display element corresponding to the
green light source is also an important factor. When d.sub.G is made
large, the scattering property when no electric field is applied is
improved. However, when d.sub.G is too large, a high voltage is needed to
obtain a sufficient transparent characteristic when an electric field is
applied, whereby there cause problems that consumption power is increased,
the conventional active element and driving IC for TN display element can
not be used, etc.
Further, when d.sub.G is made small, the scattering property when no
electric field is applied is decreased even though a high transparent
characteristic can be obtained at a low voltage. Accordingly, d.sub.G
(.mu.m) should satisfy the above-mentioned equation (4B) in order that the
scattering property when no electric field is applied is compatible with
the high transparent characteristic when an electric field is applied.
In order to uniform the characteristics of the liquid crystal display
element for each color, the values .DELTA.n.multidot.R/.lambda. or
.DELTA.n.multidot.d.sup.2 /.lambda. of the liquid crystal display elements
should be substantially matched. Specifically, the following relations:
.DELTA.n.sub.i .multidot.R.sub.i /.lambda.i.apprxeq..DELTA.n.sub.j
.multidot.R.sub.j /.lambda..sub.j ( 6)
and
d.sub.i /R.sub.i .apprxeq.d.sub.j /R.sub.j ( 7)
should be satisfied, or, the following relation should be satisfied:
.DELTA.n.sub.i .multidot.d.sub.i.sup.2 /.lambda..sub.i
.apprxeq..DELTA.n.sub.j .multidot.d.sub.j.sup.2 /.lambda..sub.j ( 8)
By matching the light phases under the conditions given by the
above-mentioned equations (6) and (7), it is possible to substantially
match the scattering intensity caused by the liquid crystal particles to
each color, to substantially match the voltage-transmittance
characteristics in an OFF state or a half tone display state, and to
obtain a display having good chromatic balance.
In practice, a colored display having better chromatic balance can be
obtained by a driving circuit for fine adjustment.
The characteristics for each color can also be uniform by letting the
average particle diameter of the liquid crystal constant for each color as
shown in the equation (8) so that the value .DELTA.n.sub.x
.multidot.d.sub.x.sup.2 /.lambda..sub.x is matched. Accordingly, color
correction can be carried by using the equations (6) and (7), or the
equation (8) in a paired liquid crystal display elements for which the
characteristics have to be matched.
It is also possible that when three or more liquid crystal display elements
are used for providing more than three colors, a part of the liquid
crystal display elements satisfies the relation as in the equations (6)
and (7), and the other part satisfies the relation as in the equation (8).
Further, when more than three liquid crystal display elements are used for
more than three colors and if there is a little difference of color to be
corrected between certain colors, the color correction of the colors
having a large color difference can be carried out by using the equations
(6) and (7), or the equation (8). Specifically, when three kinds of color
R, G and B are used, the ideal color correction can be attained if the
color correction is carried out for all three liquid crystal display
elements so as to satisfy the equations (6) and (7), or the equation (8).
However, the color correction should be carried out for at least a pair of
liquid crystal display elements among the three liquid crystal display
elements by using the equations (6) an (7), or the equation (8). More
specifically, of the following three sets of equations:
.DELTA.n.sub.R .multidot.R.sub.R /.lambda..sub.R .apprxeq..DELTA.n.sub.G
.multidot.R.sub.G /.lambda..sub.G and d.sub.R /R.sub.R .apprxeq.d.sub.G
/R.sub.G
.DELTA.n.sub.R .multidot.R.sub.R /.lambda..sub.R .apprxeq..DELTA.n.sub.B
.multidot.R.sub.B /.lambda..sub.B and d.sub.R /R.sub.R .apprxeq.d.sub.B
/R.sub.B
and
.DELTA.n.sub.G .multidot.R.sub.G /.lambda..sub.G .multidot..DELTA.n.sub.B
.multidot.R.sub.B /.lambda..sub.B and d.sub.G /R.sub.G .apprxeq.d.sub.B
/R.sub.B
at least one set of equations should be satisfied. Or, of the following
three equations:
.DELTA.n.sub.R .multidot.d.sub.R.sup.2 /.lambda..sub.R
.apprxeq..DELTA.n.sub.G .multidot.d.sub.G.sup.2 /.lambda..sub.G
.DELTA.n.sub.R .multidot.d.sub.R.sup.2 /.lambda..sub.R
.apprxeq..DELTA.n.sub.B .multidot.d.sub.B.sup.2 /.lambda..sub.B
and
.DELTA.n.sub.G .multidot.d.sub.G.sup.2 /.lambda..sub.G
.apprxeq..DELTA.n.sub.B .multidot.d.sub.B.sup.2 /.lambda..sub.B
at least one set of the equations should be satisfied.
When color correction is carried out for all three colors R, G and B, the
equations (6), (7) and (8) are expressed as follows:
.DELTA.n.sub.R .multidot.R.sub.R /.lambda..sub.R .apprxeq..DELTA.n.sub.G
.multidot.R.sub.G /.lambda..sub.G .apprxeq..DELTA.n.sub.B
.multidot.R.sub.B /.lambda..sub.B ( 6B)
and
d.sub.R /R.sub.R .apprxeq.d.sub.G /R.sub.G .apprxeq.d.sub.B /R.sub.B ( 7A)
or
.DELTA.n.sub.R .multidot.d.sub.R.sup.2 /.lambda..sub.R
.apprxeq..DELTA.n.sub.G .multidot.d.sub.G /.lambda..sub.G.sup.2
.apprxeq..DELTA.n.sub.B .multidot.d.sub.B /.lambda..sub.B.sup.2 ( 8A)
Further, when the color correction is carried out for all three colors, it
is possible to carry out the color correction for the colors R and G by
using the equations (6) and (7) and for colors G and B by using the
equation (8).
In particular, for the color corrections among R, G and B colors, since the
optical color characteristics of red (R) color is generally very different
from that of green (G) color or blue (B) color, the correction in color
between R and G or between R and B is most important. Accordingly, it is
possible that the color correction between R and G or R and B should be
made by using the equations (6) and (7) or the equation (8) while the
liquid crystal display element for the G color is the same as the liquid
crystal display element for the B color wherein the color correction
between G and B is carried out by using the driving circuit (which
requires more precise control of the voltage transmittance characteristics
in a gray scale). In this case, it is unnecessary to prepare three kinds
of liquid crystal display element as the liquid crystal display elements
for the R, G and B colors, and it is enough to manufacture two kinds of
liquid crystal display element. Accordingly, it is advantageous in
manufacturing cost.
Although the contrast ratio under the condition of the equation (8) is more
disadvantageous than that under the condition of the equations (6) and
(7), the scattering property to each of the colors can be substantially
uniform, and a display having good chromatic balance can be obtained. In
this case, it is possible to unify the characteristics for each color by
adjusting the gap between the electrode substrates if the same liquid
crystal is used for each of the colors, the liquid crystal display element
can be easily manufactured, and it is possible to obtain a multicolored
display having good chromatic balance with use of a single liquid crystal
display element when it is combined with a color filter. When the same
liquid crystal is used and a color filter is used, the equation (8) can be
modified into
d.sub.i.sup.2 /.lambda..sub.i .apprxeq.d.sub.j.sup.2 /.lambda..sub.j
(i.noteq.j) (8B)
When the color filter is used, the gap between the electrode substrates
should be uniform at each color filters for each color in accordance with
the equation (8B), whereby a display having good chromatic balance can be
obtained.
When three kinds of color R, G and B are used in the above-mentioned case,
the equation (8B) can be expressed as follows:
d.sub.R.sup.2 /.lambda..sub.R .apprxeq.d.sub.G.sup.2 /.lambda..sub.G
.apprxeq.d.sub.B.sup.2 /.lambda..sub.B ( 8C)
In the above-mentioned case too, it is possible that, for instance,
correction is not carried out by adjusting the electrode gap between G and
B, but correction is made only between R and G, and between R and B, while
color correction between G and B is carried out by using the driving
circuit. In this case, the equation (8B) is modified to be d.sub.R.sup.2
/.lambda..sub.R .apprxeq.d.sub.G.sup.2 /.lambda..sub.G or d.sub.R.sup.2
/.lambda..sub.R .apprxeq.d.sub.B.sup.2 /.lambda..sub.B.
The particle diameter of the liquid crystal which renders the intensity of
scattering at an OFF time is deeply concerned with .lambda. and .DELTA.n,
and the intensity of scattering per unit quantity of operable liquid
crystal is determined by .DELTA.nR/.lambda.. Accordingly, when the
characteristic of the liquid crystal for each color is made uniform by
using the equation (6) and (7) and the same liquid crystal is used for
each color, the average particle diameter of the liquid crystal should be
greater when the liquid crystal is used at the side of longer wavelength.
In consideration of the characteristic of the liquid crystal that the
response time becomes longer as the average particle diameter becomes
larger, it is desirable that the liquid crystal used at the side of longer
wavelength has a greater value of .DELTA.n. The liquid crystal used may be
selected taking account of the relation of the average particle diameter
to the viscosity, the elastic constant and the specific dielectric
anisotropy expressed in the equation (1), and a display of moving picture
having uniform characteristics for each color is obtainable in response to
the response characteristic, driving voltage and contrast ratio suitable
for the liquid crystal used.
It is preferable that the refractive index anisotropy .DELTA.n of the
liquid crystal used is .DELTA.n>0.18 as mentioned before. When a different
liquid crystal is used for a different color, each of the liquid crystal
used should satisfies the above-mentioned equations.
When the correction of the chromatic balance is conducted under the
conditions of the equations (6) and (7) or the equation (8), the
refractive index anisotropy for each color can be determined within the
above-mentioned ranges. When .lambda..sub.i >.lambda..sub.j, it is
preferable to satisfy the relation of .DELTA.n.sub.j
.ltoreq..DELTA.n.sub.i. Specifically, when three colors R, G and B are
used as color light sources, it is preferable to be .DELTA.n.sub.B
.ltoreq..DELTA.n.sub.G .ltoreq..DELTA.n.sub.R.
The condition of .DELTA.n.sub.B .apprxeq..DELTA.n.sub.G
.apprxeq..DELTA.n.sub.R means that the value .DELTA.n is substantially
uniform in the liquid crystal display element for each color, and this
provides such an advantage that the same liquid crystal can be used for
each of the liquid crystal display elements. In this case, the
characteristics of the liquid crystal display elements can be corrected by
adjusting the average particle diameter of the liquid crystal and the
electrode gap in accordance with the equations (6) and (7), or by
adjusting the electrode gap in accordance with the equation (8) or (8B).
Under the condition of .DELTA.n.sub.B <.DELTA.n.sub.G <.DELTA.n.sub.R, the
liquid crystal of the liquid crystal display element which is used in a
long wavelength region has a larger value of .DELTA.n. Accordingly, it is
unnecessary to considerably change the construction of the liquid crystal
polymer composite material and the electrode gap for each color. In
particular, when the value .DELTA.n/.lambda. substantially agrees with
each other for each color, it is possible to obtain good chromatic balance
by using the liquid crystal polymer composite materials which have the
substantially same construction and the substantially same electrode gap
for the liquid crystal display elements.
The condition of .DELTA.n.sub.B .apprxeq..DELTA.n.sub.G <.DELTA.n.sub.R or
.DELTA.n.sub.B <.DELTA.n.sub.G .apprxeq..DELTA.n.sub.R means that the
characteristics of three colors are substantially agreed with each other
by using two kinds of liquid crystal. The characteristics of each color
can be corrected by adjusting the average particle diameter of the liquid
crystal and the electrode gap in accordance with the equations (6) and (7)
or by adjusting the electrode gap in accordance with the equation (8).
The absolute value of the gap d between the electrode substrates can be
selected depending on the applied voltage used so that the brightness of
the display and the contrast ratio become the optimum. It is preferable
that the maximum applied voltage and the gap between the electrode
substrates are in the range as follows:
0.6R.multidot.V<d<1.2R.multidot.V (5)
In a case of a multi-colored display, the active matrix liquid crystal
display element for each color should satisfy:
0.6R.sub.x .multidot.V.sub.x <d.sub.x <1.2R.sub.x .multidot.V.sub.x ( 5A)
As far as the maximum applied voltage and the gap between the electrode
substrates assume values in the above-mentioned range, it is possible to
obtain a display having high contrast ratio even by using the conventional
active element for TN and driving IC.
The value d in the equation (5) can be suitably determined in the relation
between the specific dielectric anisotropy .DELTA..epsilon.
(=.epsilon.//-.epsilon..perp.) of the liquid crystal used and the elastic
constant. Generally, the liquid crystal having a larger value
.DELTA..epsilon. (.DELTA..epsilon.>5) should be used so that the value d
becomes maximum in the range that a sufficient transparent characteristic
can be obtained by the maximum effective application voltage.
In the active matrix liquid crystal display element using the liquid
crystal polymer composite material which provides a transparent state when
a voltage is applied and a scattering state when no electric field is
applied, the liquid crystal display element which satisfies the conditions
of the equations (1) and (2) can provide, by using the conventional active
element for TN or conventional driving IC, a display having a high
contrast ratio and brightness by the application of the voltage ranging in
the equation (5).
In the case of the multi-colored display, the liquid crystal display
element which satisfies the conditions of the equations (1A), (2A) and the
equations (6) and (7) or the conditions of the equations (1A), (2A) and
(8), or the equations (1), (2) and (8B) can provide, by using the
conventional active element for TN and driving IC, a projection display of
colored moving picture having high contrast ratio, brightness and good
chromatic balance in a range of voltage expressed in the equation (5A).
Specifically, it is possible to obtain a display wherein the contrast
ratio is 100 or higher, the transmittance when an electric field is
applied is 70% or higher and the response time at the time of gray scale
display is 200 msec or lower.
When the liquid crystal display element is used for a reflection type
display apparatus, the scattering property in scattering mode increases
since light passes twice through the liquid crystal polymer composite
material. Accordingly, it is possible to reduce the value dx within the
range as in the equation (4A) or (4B), and the maximum driving voltage
determined in accordance with the equation (5A) can be also reduced.
In order to improve the scattering property when no electric field is
produced, it is effective to increase the volume fraction .PHI. of the
liquid crystal which is operable in the liquid crystal polymer composite
material. The range of .PHI.>20% is preferred. In order to obtain higher
scattering property, it is preferable to be .PHI.>35%, more preferably
.PHI.>45%. On the other hand, when the value .PHI. is excessively high,
the stability in structure of the liquid crystal polymer composite
material becomes inferior. Accordingly, it is preferable that .PHI.<70%.
The liquid crystal display element of the present invention shows, when no
electric field is applied, a scattering state (i.e., an opaque state) due
to a difference in refractive index between the liquid crystal not in an
oriented condition and the polymer matrix. Accordingly, when the liquid
crystal is used for a projection type display apparatus as in the present
invention, light is scattered by a portion of the liquid crystal display
element at which no electrode is located, and the portion looks dark
because light does not reach a projection screen even when no light
shielding layer is provided at the portion other than picture elements. In
order to prevent light from leaking from any other portion of the liquid
crystal display element than the picture element electrodes, it is
unnecessary to provide a light shielding layer for the portion other than
the picture element electrodes. Accordingly, there is an advantage that
the step of forming the light shielding layer is unnecessary.
An electric field is applied to a desired picture element. At the picture
element portion to which the electric field is applied, the liquid crystal
is oriented so that the ordinary refractive index (n.sub.0) of the liquid
crystal and the refractive index (n.sub.p) of the polymer matrix coincide
with each other. Accordingly, the liquid crystal display element presents
a transparent state, and light is transmitted through desired picture
elements to thereby provide a bright display on a projection screen.
If the polymer is cured during the curing step while a sufficiently high
voltage is applied only to a specified portion of the element, the portion
is formed to have a normally light transparent state. Accordingly, in a
case that there is to form a fixedly display portion, such a normally
transparent portion may be formed.
In the active matrix liquid crystal display element of the present
invention, a colored display can be attained by providing a color filter.
Color filters having different three colors may be provided in a single
liquid crystal display element, or a color filter for a specified color
may be provided in a single liquid crystal display element and three
liquid crystal display elements having different color filters may be used
in combination. The color filter may be provided on the surface having
electrodes of the substrate or may be provided at the outside of the
substrate.
Further, dye, pigment or the like may be mixed into the liquid crystal
polymer composite material to conduct a color display.
Claims
What is claimed is:
1. An active matrix liquid crystal display element comprising an active
matrix substrate having an active element for each electrode for picture
element, a counter electrode substrate provided with a counter electrode
and a liquid crystal polymer composite material in which a nematic liquid
crystal having a positive dielectric anisotropy is dispersed and held in a
polymer matrix, said liquid crystal polymer composite material being held
between the active matrix substrate and the counter electrode substrate
wherein the refractive index of the polymer matrix substantially agrees
with the ordinary refractive index (n.sub.0) of the liquid crystal used,
characterized in that the refractive index anisotropy .DELTA.n of the
nematic liquid crystal used is 0.18 or higher, and the average particle
diameter R(.mu.m) of the liquid crystal dispersed and held in the polymer
matrix, and the specific dielectric anisotropy .DELTA..epsilon., the
elastic constant K33(10.sup.-12 N) and the viscosity .eta. (cSt) of the
liquid crystal satisfy the following relations:
.DELTA.n.sup.2 .multidot..DELTA..epsilon./(K33.multidot..eta.)>0.0011 (1)
and
4(K33/.eta.).sup.0.5 >R>(K33/.DELTA..epsilon.).sup.0.5 ( 2)
2. The active matrix liquid crystal display element according to claim 1,
wherein the relations of
.DELTA.n.sup.2 .multidot..DELTA..epsilon./(K33.multidot..eta.)>0.0014 (1B)
are satisfied.
3. The active matrix liquid crystal display element according to claim 1,
wherein the refractive index anisotropy .DELTA.n of the liquid crystal and
the average particle diameter R of the liquid crystal held in the polymer
matrix satisfy the relation of
0.2<R.multidot..DELTA.n<0.7 (3)
4. The active matrix liquid crystal display element according to claim 1,
wherein the gap d (.mu.m) between the counter electrode and the picture
element electrode, and the maximum effective voltage V (V) applied to the
liquid crystal polymer composite material satisfy the following relations:
3R<d<9R (4)
0.6R.multidot.V<d<1.2R.multidot.V (5)
5. The active matrix liquid crystal display element according to claim 1,
wherein resin used for the liquid crystal polymer composite material is a
photo-curable compound, and said liquid crystal polymer composite material
is obtained by curing the compound by irradiating light to a solution
obtained by uniformly dissolving the photo-curable compound in the liquid
crystal.
6. A projection type active matrix liquid crystal display apparatus which
comprises a projection light source, a projection optical system and the
active matrix liquid crystal display element as claimed in claim 1.
7. The projection type active matrix liquid crystal display apparatus
according to claim 6, wherein in said active matrix liquid crystal display
element, the refractive index anisotropy .DELTA.n of the liquid crystal
and the average particle diameter R of the liquid crystal held in the
polymer matrix satisfy the relation of
0.2<R.multidot..DELTA.n<0.7 (3)
8. The projection type active matrix liquid crystal display apparatus
according to claim 6, wherein in said active matrix liquid crystal display
element, the gap d (.mu.m) between the counter electrode and the picture
element electrodes, and the maximum effective voltage V (V) applied to the
liquid crystal polymer composite material satisfy the following relations:
3R<d<9R (4)
and
0.6R.multidot.V<d<1.2R.multidot.V (5)
9. The projection type active matrix liquid crystal display apparatus
according to claim 6, wherein resin used for the liquid crystal polymer
composite material is a photo-curable compound, and the active matrix
comprises the liquid crystal polymer composite material obtained by curing
the compound by irradiating light to a solution obtained by uniformly
dissolving the photo-curable compound in the liquid crystal.
10. A projection type active matrix liquid crystal display apparatus
comprising a plurality of color light sources, a plurality of active
matrix liquid crystal display elements for receiving light from each of
the color light sources and a projection optical system which synthesizes
and projects light emitted from the active matrix liquid crystal display
elements, characterized in that each of the active matrix liquid crystal
display elements comprises an active matrix substrate having an active
element for each electrode for picture element, a counter electrode
substrate provided with a counter electrode and a liquid crystal polymer
composite material in which a nematic liquid crystal having a positive
dielectric anisotropy is dispersed and held in a polymer material, said
liquid crystal polymer composite material being held between the active
matrix substrate and a counter electrode substrate provided with the
counter electrode, and the refractive index of the polymer matrix
substantially agrees with the ordinary refractive index (n.sub.0) of the
liquid crystal used, and that the average particle diameter R.sub.x
(.mu.m) of the liquid crystal corresponding to each color, which is
dispersed and held in the polymer matrix, the gap d.sub.x (.mu.m) between
the counter electrode and the picture element electrode, the specific
dielectric anisotropy .DELTA..epsilon..sub.x, the elastic constant
K33.sub.x (10.sup.-12 N), the viscosity .eta..sub.x (cSt), and the
refractive anisotropy .DELTA.n.sub.x of the liquid crystal and the main
wavelength .lambda..sub.x (.mu.m) of each of the colors satisfy the
following relations:
.DELTA.n.sub.x.sup.2 .multidot..DELTA..epsilon..sub.x /(K33.sub.x
.multidot..eta..sub.x)>0.0011 (1A)
and
4(K33.sub.x /.eta..sub.x).sup.0.5 >R.sub.x >(K33.sub.x
/.DELTA..epsilon..sub.x).sup.0.5 ( 2A)
wherein at least a pair of the active matrix liquid crystal display
elements satisfies the relations:
.DELTA.n.sub.i .multidot.R.sub.i /.lambda..sub.i .apprxeq..DELTA.n.sub.j
.multidot.R.sub.j /.lambda..sub.j ( 6)
and
d.sub.i /R.sub.i .apprxeq.d.sub.j /R.sub.j ( 7)
where i.noteq.j, or it satisfies the relation:
.DELTA.n.sub.i .multidot.d.sub.i.sup.2 /.lambda..sub.i
.apprxeq..DELTA.n.sub.j .multidot.d.sub.j.sup.2 /.lambda..sub.j ( 8)
where i.noteq.j.
11. The projection type active matrix liquid crystal display apparatus
according to claim 10, wherein the relations of
.DELTA.n.sub.x.sup.2 .multidot..DELTA..epsilon..sub.x.sup.2 /(K33.sub.x
.multidot..eta..sub.x)>0.0014 (1C)
are satisfied.
12. The projection type active matrix liquid crystal display apparatus
according to claim 10, wherein said color light sources are R, G an B
color light sources, x satisfies both the equations (1A) and (2C) for each
of the R, G and B colors, and wherein the relations:
.DELTA.n.sub.R .multidot.R.sub.R /.lambda..sub.R .apprxeq..DELTA.n.sub.G
.multidot.R.sub.G /.lambda..sub.G .apprxeq..DELTA.n.sub.B
.multidot.R.sub.B /.lambda..sub.B ( 6A)
and
d.sub.R /R.sub.R .apprxeq.d.sub.G /R.sub.G .apprxeq.d.sub.B /R.sub.B ( 7A)
are satisfied, or the relation:
.DELTA.n.sub.R .multidot.d.sub.R.sup.2 /.lambda..sub.R
.apprxeq..DELTA.n.sub.G .multidot.d.sub.G.sup.2 /.lambda..sub.G
.apprxeq..DELTA.n.sub.B .multidot.d.sub.B.sup.2 /.lambda..sub.B ( 8A)
is satisfied.
13. The projection type active matrix liquid crystal display apparatus
according to claim 10, wherein when the refractive index anisotropy
.DELTA.n.sub.x of the liquid crystal used for the active matrix liquid
crystal display element assumes .lambda..sub.i >.lambda..sub.j, the
relation of .DELTA.n.sub.j .ltoreq..DELTA.n.sub.i is satisfied.
14. The projection type active matrix liquid crystal display apparatus
according to claim 10, wherein the refractive index anisotropy
.DELTA.n.sub.x of the liquid crystal used for each color and the average
particle diameter R.sub.x of the liquid crystal held in the polymer matrix
satisfy the relation of
0.2<R.sub.x .multidot..DELTA.n.sub.x <0.7 (3A)
15. The projection type active matrix liquid crystal display apparatus
according to claim 10, wherein the average particle diameter R.sub.x
(.mu.m) of the liquid crystal for each color, the gap d.sub.x between the
counter electrode and the picture element electrodes and maximum effective
voltage V.sub.x (V) applied to the liquid crystal polymer composite
material satisfy the relations:
3R.sub.x <d.sub.x <9R.sub.x ( 4A)
and
0.6R.sub.x .multidot.V.sub.x <d.sub.x <1.2R.sub.x .multidot.V.sub.x ( 5A)
16. An active matrix liquid crystal display element comprising R, G and B
color filters, an active matrix substrate having an active element for
each picture element electrode, a counter electrode substrate provided
with a counter electrode and a liquid crystal polymer composite material
in which a nematic liquid crystal having a positive dielectric anisotropy
is dispersed and held in a polymer matrix wherein the refractive index of
the polymer matrix substantially agrees with the ordinary refractive index
(n.sub.0) of the liquid crystal used, said liquid crystal polymer
composite material being held between the active matrix substrate and the
counter electrode substrate, characterized in that the average particle
diameter R (.mu.m) of the liquid crystal dispersed and held in the polymer
matrix, the specific dielectric anisotropy .DELTA..epsilon., the elastic
constant K33(10.sup.-12 N), the viscosity .eta.(cSt) and the refractive
index anisotropy .DELTA.n of the liquid crystal and the main wavelength
.lambda..sub.x (.mu.m) of each color satisfy the relations:
.DELTA.n.sup.2 .multidot..DELTA..epsilon./(K33.multidot..eta.)>0.0011 (1)
and
4(K33/.eta.).sup.0.5 >R>(K33/.DELTA..epsilon.).sup.0.5 ( 2B)
and that at least two colors among the R, G and B colors satisfy the
relation:
d.sub.i.sup.2 /.lambda..sub.i .apprxeq.d.sub.j.sup.2 /.lambda..sub.j ( 8B)
where i.noteq.j.
17. The active matrix liquid crystal display element according to claim 16,
wherein the relations;
.DELTA.n.sup.2 .multidot..DELTA..epsilon./(K33.multidot..eta.)<0.0014 (1B)
are satisfied.
18. The active matrix liquid crystal display element according to claim 16,
wherein the refractive index anisotropy .DELTA.n of the liquid crystal and
the average particle diameter R of the liquid crystal satisfy the relation
of
0.2<R.multidot..DELTA.n<0.7 (3)
19. The active matrix liquid crystal display element according to claim 16,
wherein the average particle diameter R of the liquid crystal and the gap
d.sub.G (.mu.m) between the counter electrode and the picture element
electrode for the color of G satisfies the relation of
3R<d.sub.G <9R (4B)
20. A projection type active matrix liquid crystal display apparatus which
comprises a projective light source, a projective optical system and the
active matrix liquid crystal display element claimed in claim 16.
Description
In drawings:
FIGS. 1 and 2 are respectively diagrams showing the basic construction of
embodiments of the projection type active matrix liquid crystal display
apparatus according to the present invention; and
FIG. 3 is a diagram in cross section which shows the basic construction of
an embodiment of the active matrix liquid crystal display element
according to the present invention.
Preferred embodiments of the active matrix liquid crystal display element
and the projection type active matrix liquid crystal display apparatus of
the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an embodiment of the projection type active
matrix liquid crystal display apparatus in which dichroic prisms are used,
in accordance with the present invention.
In FIG. 1, reference numeral 1 designates a light source, numeral 2
designates a concave mirror, numeral 3 designates a condenser lens,
numeral 4 designates a color splitting dichroic prism, numerals 5A, 5B,
5C, 5D designate mirrors, the elements 1 through 5D constituting a color
light source, numerals 6A, 6B, 6C designates active matrix liquid crystal
elements each having a liquid crystal polymer composite material
corresponding to each color, numeral 7 designates a synthesizing dichroic
prism, numeral 8 designates a projection lens, numeral 9 designates an
aperture for removing light other than straight-forward light and numeral
10 designates a projection screen, the elements 7 through 9 constituting a
projection optical system.
FIG. 2 is a diagram showing an embodiment of the projection type active
matrix liquid crystal display apparatus of the present invention wherein
no dichroic prism is used.
In FIG. 2, reference numeral 11 designates a light source, numeral 12
designates a concave mirror, numeral 3 designates condenser lens, numerals
15A, 15B, 15C designate dichroic mirrors, the elements 11 through 15C
constituting a color light source, numerals 16A, 16B, 16C designate active
matrix liquid crystal display elements each having a liquid crystal
polymer composite material corresponding to each color, numerals 18A, 18B,
18C designate projection lenses provided for each color, numerals 19A,
19B, 19C designate apertures for removing light other than
straight-forward light which are respectively provided for different
colors, and numeral 20 designates a projection screen, the elements
18A-19C constituting a projection optical system.
FIG. 3 is a cross-sectional view showing an embodiment of the active matrix
liquid crystal display element used for the projection type active matrix
liquid crystal display apparatus of the present invention.
In FIG. 3, reference numeral 21 designates an active matrix liquid crystal
display element, numeral 22 designates a substrate such as glass, plastics
or the like which is used for an active matrix substrate, numeral 23
designates a picture element electrode such as ITO (In.sub.2 O.sub.3
--SnO.sub.2), SnO.sub.2 or the like, numeral 24 designates an active
element such as transistor, a diode, a nonlinear resistance element or the
like, numeral 25 designates a substrate such as glass, plastics or the
like which is used for a counter electrode substrate, numeral 26
designates a counter electrode such as ITO, SnO.sub.2 or the like, and
numeral 27 designates a liquid crystal polymer composite material
interposed between the substrate 22, 25.
In a case of using a three-terminal element such as TFT (thin film
transistor) as the active element in accordance with the present
invention, a solid electrode in common with all picture elements may be
disposed for the counter electrode substrate. In the case of using a
two-terminal element such as an MIM element or a PIN diode, however, the
counter electrode substrate is applied with a stripe-like patterning.
In the case of using TFT as the active element, silicon is suitable as the
semiconductor material. Polycrystalline silicon is particularly preferred
since it has less photosensitivity as in amorphous silicon and,
accordingly, does not cause erroneous operation even without shielding
light from a light source by means of a light shielding film. In the case
of using polycrystalline silicon for the projection type liquid crystal
display apparatus in the present invention, a strong light source for
projection can be utilized and a bright display is obtainable.
In the case of the conventional TN type liquid crystal display element, a
light shielding film is often formed between picture elements so as to
suppress the leakage of light from the portion between the picture
elements, and a light shielding film can be formed to the active element
at the same time of forming the light shielding film between the picture
elements. Accordingly, formation of the light shielding film to the active
element gives no substantial effect on the entire steps. Namely, if the
polycrystalline silicon is used for the active element and the light
shielding film is not formed to the active element portion, the number of
steps can be decreased if it is required to form the light shielding film
at the portion between the picture elements.
On the contrary, in the present invention, since the liquid crystal polymer
composite material wherein the refractive index of the polymer matrix
substantially agrees with the ordinary refractive index (n.sub.0) of the
liquid crystal used, is used as described before, light is scattered at
the area not applied with the electric field, and it appears dark on the
projection screen. Accordingly, there is no requirement for forming the
light shielding film in the portion between the picture elements.
Therefore, in the case of using the polycrystalline silicon as the active
element, there is no requirement for forming the light shielding film at
the active element portion, and accordingly, the step of forming the light
shielding film can be eliminated or severe requirements to the light
shielding film can be reduced, whereby the number of manufacturing steps
can be reduced and the productivity is improved.
Even in the case of using the amorphous silicon, if the light shielding
film is formed at the semiconductor portion, the active matrix liquid
crystal display element of the present invention can be used.
Further, the electrodes used are usually transparent electrodes. In the
case of using the electrodes for a reflection type liquid crystal display
apparatus, however, a reflection electrode made of a material such as Cr,
Al or the like may be used.
In the liquid crystal display element and the liquid crystal display
apparatus according to the present invention, an infrared ray cut filter
or UV-ray cut filter or the like may be used in a lamination form, or
characters, figures or the like may be printed, or a plurality of liquid
crystal display element may be used.
Further, in the present invention, a protective plate such as glass plate,
a plastic plate or the like may be overlaid on or at the outside of the
liquid crystal display element. The protective plate reduces a danger of
the breakage of the display element when the surface of the element is
pushed, whereby the safety of the display element is improved.
In the case of using a photo-curable compound as an uncured polymer
constituting the liquid crystal polymer composite material as described
above in the present invention, photo-curable vinyl compound is preferably
used.
Specifically, there can be exemplified a photocurable acryl compound and,
particularly, those containing acryl oligomer which is curable upon
polymerization under the irradiation of light are particularly preferred.
The liquid crystal used in the present invention may be a nematic liquid
crystal having a positive dielectric anisotropy or such a liquid crystal
that the refractive index of the polymer matrix agrees with the ordinary
refractive index (n.sub.0) of the liquid crystal. Such liquid crystal may
be used solely or may be used as a composition, and the use of a
composition can be advantageous for satisfying various demands such as for
working temperature range, working voltage, etc.
When the photo-curable compound is used for the liquid crystal polymer
composite material, it is preferable to uniformly dissolve the
photo-curable compound in the liquid crystal. The cured material after
exposure to light can not be dissolved or is hardly dissolved. When the
above-mentioned composition is used, it is desirable to use the liquid
crystal having a closer value in solubility.
The liquid crystal polymer composite material is prepared as follows. For
instance, an active matrix substrate and a counter electrode substrate are
arranged, and the surfaces with electrodes of the substrates are opposed;
the circumferential portions of the two substrates opposed are sealed with
a sealing material; a mixed solution of uncured liquid crystal polymer
composite material is injected through an injection port followed by
sealing the injection port. Or a mixture of uncured compound and liquid
crystal is supplied to one of the substrates, followed by overlaying the
other so as to oppose to each other, in the same manner as the
conventional preparation of the liquid crystal display element.
For the liquid crystal display element of the present invention, di-chroic
dye, dye or pigment may be added to the liquid crystal, or a colored
material may be used as a curable compound.
In the present invention, when the liquid crystal in the liquid crystal
polymer composite material is utilized as the solvent, and the
photo-curable compound is cured by the exposure to light it is unnecessary
to evaporate solvent or water which is needless at the curing time.
Accordingly, in this case, the conventional method of preparation of the
injection of liquid crystal to the cell can be employed because the
curable compound is cured in an enclosed system. The curing of the curable
compound in the enclosed system provides high reliability. This can be
further assured by the effect obtained by bonding the two substrates with
the photocurable compound.
In the present invention, since the liquid crystal polymer composite
material is used, a possibility that the upper and lower transparent
electrodes may short-circuit can be reduced, and it is unnecessary to
strictly control the orientation of the liquid crystal and the substrate
gap as required for the conventional TN type display element. Accordingly,
the liquid crystal display element capable of controlling a transparent
state and a scattering state can be effectively produced.
In the liquid crystal display element of the present invention, it is
preferable to laminate a protective plate such as plastics or glass at the
outside of the substrate in a case that the substrate is made of plastics
or a thin glass plate.
The liquid crystal display apparatus of the present invention can be drived
with the maximum effective voltage or lower as in the before-mentioned
equation (5) or (5A). Generally the liquid crystal display apparatus is
drived so that the maximum effective voltage is applied to the liquid
crystal polymer composite material between picture element electrodes and
a counter electrode.
The color light source, the projection optical system, the projection
screen and so on used in the present invention may be a conventionally
used light source, projection optical system, projection screen and so on.
It is enough that the active matrix liquid crystal display element is
disposed between the color light source and the projection optical system.
In this case, the projection optical system may be used in such a manner
that images from the plurality of the active matrix liquid crystal display
elements are synthesized with use of an optical system and the synthesized
image is projected, as shown in FIG. 1. Alternatively, as shown in FIG. 2,
the images of the plurality of the active matrix liquid crystal elements
are respectively projected on the projection screen so that the images are
synthesized on the projection screen.
In the above-mentioned embodiments, the color light source is obtained by
subjecting light from a single light source to color splitting. However, a
plurality of light sources having different colors are separately provided
so that lights of the plurality of the light sources are caused to enter
into the active matrix liquid crystal display elements.
As the light source used for the color light source, there are a halogen
lamp, a metal halide lamp, a xenone lamp and so on. Further, a concave
mirror, a condenser lens or the like may be combined with the lamp to
increase utilization of light.
In addition to the lamp or the combination of the lamp and the mirror or
lens, a cooling system may be added, or an infrared ray cut filter or UV
ray cut filter may be added, or a TV channel display devise such as LED or
the like may be added.
In particular, in the case of using the projection type display, a devise
for reducing diffusion light, e.g. an aperture or a spot as indicated by
numerals 9, 19A, 19B, 19C in FIG. 1 or 2 may be disposed on the optical
path so that the contrast ratio of display can be increased. Namely, the
device for reducing diffusion light is preferred to use such a device that
among incident light passing though the liquid crystal display element,
straight-forward light (light which has transmitted portions in which the
picture element portions are in a transparent state) is taken, and
non-straight-forward light (light scattered at portions in which the
liquid crystal polymer composite material is in a scattering state) is
diminished. Such diffusion light reducing device is preferred because the
contrast ratio can be improved. In particular, the device which does not
reduce the straight-forward light but reduces diffusion light on the
non-straight-forward light, is preferred.
The device for reducing the diffusion light may be provided between the
projection optical system and the projection screen as shown in FIGS. 1
and 2. Further, the device for reducing diffusion light may be disposed
between lenses in a case that the projection optical system is constituted
by a plurality of lenses.
The device for reducing diffusion light is not limited to the
above-mentioned aperture or spot, but may be a mirror having a small
surface area disposed on the optical path, for instance.
The focal length or the diameter of a projecting lens may be suitably
selected so as to remove scattering light, without using a specially
arranged aperture.
Further, a microlens system can be used. Specifically, a combination of a
microlens array and a spot array in which fine holes are formed in array
may be disposed at the side of the projection optical system with respect
to the liquid crystal display element to thereby remove needless
scattering light. This arrangement has an advantage of reducing the entire
size of the projection type display apparatus because the optical path
length necessary for removing scattering light can be remarkably
shortened. In order to reduce the optical path length, the installation of
the scattering light removing system in the projection optical system is
effective way. The structure of projection type display apparatus in which
the scattering light removing system is installed in the projection
optical system is simpler than the structure in which the projection
optical system and the scattering light removing system are independently
disposed, whereby the entire size of the apparatus can be reduced.
These systems may be used in combination with a mirror, a dichroic mirror,
a prism, a dichroic prism, a lens and so on to synthesize a picture image
and to display a colored image. Further, a colored picture image is
obtainable by combining the optical system with a color filter.
The ratio of the scattered light component and the straight-forward light
component reaching on the projection screen can be controlled by adjusting
the diameter of the spot or the mirror and the focal length of the lens,
so that a desired contrast ratio of display and the brightness in display
can be obtained.
When the device for reducing diffusion light such as an aperture, light
entering from the projection light source to the liquid crystal display
element should be parallel in order to increase the brightness of display.
For this, it is preferable to constitute a projection light source by
combining a light source capable of providing high brightness (which
should be a point light source), a concave mirror, a condenser lens and so
on.
Description has been made mainly as to the projection type display
apparatus having a transparent type structure. However, the present
invention is applicable to a projection type display apparatus having a
reflection type structure wherein a small mirror is disposed, instead of a
spot, to take out only necessary light.
In the present invention having the above-mentioned construction, the
maximum effective voltage V applied to the liquid crystal polymer
composite material can be 10V or lower and high response characteristic is
obtainable even in a half tone display. Accordingly, a display of moving
picture can be easily attained by using an active element and driving IC
which has been used for the conventional TN active matrix liquid crystal
display element. Further, in accordance with the present invention, a gray
scale display having good chromatic balance and beautiful colors is
possible without installing a special correction circuit for the driving
circuit.
In the following, the present invention will be described more in detail in
connection with various examples.
EXAMPLE 1
Chrome was vapor-deposited to a thickness of 60 nm on a glass substrate
("7059" substrate manufactured by Corning), and the article was patterned
to form gate electrodes. Then, a silicon oxynitride film and an amorphous
silicon film were deposited by using a plasma CVD apparatus. Then, after
annealing with use of a laser, a patterning operation was conducted to
form polysilicon. Phospher-doped amorphous silicon and chrome were
deposited on the polysilicon using the plasma CVD and a vapor-deposition
apparatus. A patterning operation was conducted to cover the polysilicon
to form source electrodes and drain electrodes for the first layer.
Further, vapor-deposition of ITO was conducted. Then, the article was
patterned to form picture element electrodes. Then, chrome and aluminum
were successively vapor-deposited. A patterning operation was conducted to
form the second layer of the source electrodes, and the second layer of
the drain electrodes so as to connect the picture element electrodes with
the first layer of drain electrodes. Then, a silicon oxynitride film was
deposited to form a protective layer by using the plasma CVD apparatus to
thereby form an active matrix substrate.
A counter electrode substrate was prepared by using the same glass
substrate as used for the active matrix substrate, on the entire surface
of which an ITO electrode is formed. The counter electrode substrate and
the previously prepared active matrix substrate were disposed so as to
face the electrode surfaces of the both substrates. Spacers each having
diameter of about 11.0 .mu.m were placed in the space between the
substrates. The peripheral portions of the substrates were sealed with a
sealing material of an epoxy series resin except the location of an
injection port to produce an empty cell having a gap d.sub.G of 11.0
.mu.m.
A nematic liquid crystal having about 0.24 of .DELTA.n, about 16 of
.DELTA..epsilon., about 15 (.times.10.sup.-12 N) of K33 and about 37 cSt
of viscosity, acrylate monomer, bifunctional urethane acrylate oligomer
and a photo-cure initiator were uniformly dissolved to prepare solution of
liquid crystal polymer composite material. The solution was injected in
the cell, and the cell was exposed to UV rays to cure the liquid crystal
polymer composite material to thereby complete an active matrix liquid
crystal display element. The liquid crystal quantity, the gap between the
electrodes and the average particle diameter of the liquid crystal in the
liquid crystal display element were respectively 68 wt %, about 11 .mu.m
and about 1.6 .mu.m.
When the liquid crystal display element was drived by applying a voltage so
that the voltage applied to the liquid crystal polymer composite material
was 8 V in terms of effective value, it was found that the linear
transmittance was about 75% when a voltage of 8 V was applied, and about
0.4% when no voltage was applied. The liquid crystal display element was
combined with a projection light source and a projection optical system to
form a projection type liquid crystal display apparatus. In the projection
type liquid crystal display apparatus, a collection cone angle .delta.
(which is determined by the equation .delta.=2tan.sup.-1 (.PHI./2f), in
which .PHI. is the diameter of the aperture spot and f is the focal length
of the lens) was adjusted to 06.degree.. The apparatus was drived with a
video signal to project a picture image on a screen. As a result, a
display of moving picture was obtained without any residual image even in
a half tone display.
The above-mentioned liquid crystal display element was used for a color of
green.
In the same manner as above, a cell having d.sub.R =13.5 .mu.m and R.sub.R
=1.9 .mu.m for a color of red and a cell having d.sub.B =9.5 .mu.m and
R.sub.B =1.5 .mu.m for a color of blue were respectively prepared.
These elements were used in combination with the projection light source
and the projection optical system as shown in FIG. 1 to form a projection
type liquid crystal display apparatus. The collection cone angle .delta.
(described before) was adjusted to 6.degree.. The display apparatus was
drived with a video signal to project a picture image on the screen. As a
result, a display of moving picture having good chromatic balance and
without any residual image was obtained even in a half tone display. The
contrast ratio on the screen was about 130.
The response time (a 90% transmittance change under the condition that the
elements for R, G and B are simultaneously drived and a monochrome image
is measured) was 10 msec under the condition of 8 V.fwdarw.0 V, 15 msec
under the condition of 0 V.fwdarw.8 V, and 110 msec under the condition of
0 V.fwdarw.saturated transmittance.times.0.2 (about 16%) respectively.
COMPARATIVE EXAMPLE 1
Three liquid crystal display elements for green color were prepared in the
same manner as described in Example 1. These liquid crystal display
elements were combined with a light source having three colors R, G and B
to constitute the same projection type display apparatus as in Example 1.
The projection type display apparatus provided a generally reddish picture
image. In particular this tendency was remarkable in a half tone display.
When an electric field was removed for each of the three liquid crystal
display elements, the projection screen did not become dark but it
exhibited a dark red color. It is likely because of different threshold
voltage characteristics of the liquid crystal for R, G and B. In
examination of applied voltage-transmittance characteristics for each of
R, G and B, it was found that R exhibited the highest transmittance and B
exhibited the lowest transmittance in a half tone display region under the
application of the same voltage.
COMPARATIVE EXAMPLE
A projection type active matrix liquid crystal display element was prepared
in the same manner as described in Example 1 except that a nematic liquid
crystal was used instead of the liquid crystal polymer composite material
(whereby a TN type liquid crystal display element was obtained).
Thus prepared liquid crystal display element was used in combination with
the projection light source and the projection optical system as in
Example 1 to thereby form a projection type liquid crystal display
apparatus. The projection type liquid crystal display apparatus was drived
in the same manner as described in Example 1. The brightness of display on
the projection screen was about 1/3 as dark as the case in Example 1 and
the contrast ratio was about 100.
The response time was 25 msec under the condition of 5 V.fwdarw.0 V, 30
msec under the condition of 0 V.fwdarw.5 V, and 160 msec under the
condition of 0v.fwdarw.saturated transmittance.times.0.2 (about 6%).
EXAMPLES 2 THROUGH 4 AND COMPARITIVE EXAMPLES 3 THROUGH 5
Active matrix liquid crystal display elements were prepared in the same
manner as in Example 1 wherein the average particle diameter R of the
liquid crystal and the substrate gap d were changed.
For each of the active matrix liquid crystal display elements, the
transmittance T8v of the liquid crystal display elements when a 8 V
voltage was applied, the contrast ratio CR of an image on the screen when
it is projected on the screen with use of the projection optical system
and the response time .tau. under the condition of 0 V.fwdarw.saturated
transmittance.times.0.2 (about 16%) were respectively measured.
Example 2 and Comparative Examples 3 and 4 show examples of a monochrome
type. The following conditions were set.
R=1.3 .mu.m and d=9.5 .mu.m for Example 2
R=2.7 .mu.m and d=11.0 .mu.m for Comparative Example 3
R=0.7 .mu.m and d=11.0 .mu.m for Comparative Example 4
Examples 3 and 4 and Comparative Example 5 are of examples of multicolor
type.
The average particle diameter R.sub.x of the liquid crystal and the
substrate gap d.sub.x of the liquid crystal display elements for
respective colors were determined as follow.
______________________________________
Example 3 red: R.sub.R = 1.6 .mu.m, d.sub.R = 11.5 .mu.m
green: R.sub.G = 1.6 .mu.m, d.sub.G = 10.0 .mu.m
blue: R.sub.B = 1.6 .mu.m, d.sub.B = 9.5 .mu.m
Example 4 red: R.sub.R = 1.9 .mu.m, d.sub.R = 13.5 .mu.m
green: R.sub.G = 1.6 .mu.m, d.sub.G = 11.0 .mu.m
blue: R.sub.B = 1.6 .mu.m, d.sub.B = 10.0 .mu.m
Comparative red: R.sub.R = 3.0 .mu.m, d.sub.R = 15.5 .mu.m
Example 5 green: R.sub.G = 2.5 .mu.m, d.sub.G = 13.0 .mu.m
blue: R.sub.B = 2.3 .mu.m, d.sub.B = 11.0
______________________________________
.mu.m
The result of measurement is shown in Table 1. Examples 3 and 4 and
Comparative Example 5 respectively exhibited excellent chromatic balance.
TABLE 1
______________________________________
T8v .tau.
Example No. % CR msec
______________________________________
Example 2 70 130 100
Comparative 80 60 600
Example 3
Comparative 20 50 60
Example 4
Example 3 74 100 120
Example 4 70 120 140
Comparative 68 80 450
Example 5
______________________________________
EXAMPLE 5
Liquid crystal display elements were prepared in the substantially same
manner as Example 1 provided that the average particle diameter of liquid
crystal and the gap between the electrodes in the liquid crystal display
elements for respective colors were constant (R=1.7 .mu.m and d=11.0
.mu.m) and the physical properties of the liquid crystal were changed as
follows. Liquid crystal for R: .DELTA.n=about 0.29, .DELTA..epsilon.=about
16, K33=about 16 (.times.10.sup.-12 N), viscosity=about 52 cSt Liquid
crystal for G: .DELTA.n=about 0.24, .DELTA..epsilon.=about 16, K33=about
15 (.times.10.sup.-12 N), viscosity=about 37 cSt Liquid crystal for B:
.DELTA.n=about 0.22, .DELTA..epsilon.=about 15, K33=about 16
(.times.10.sup.-12 N), viscosity=about 34 cSt
These display elements were used in combination with the projection light
source and the projection optical system as shown in FIG. 1 to thereby
form a projection type liquid crystal display apparatus. The collection
cone angle was adjusted to 5.degree. and driving voltage was adjusted to 7
V in terms of effective value. The display apparatus was drived with a
video signal to project an image on the screen. As a result, a display of
moving picture having good chromatic balance and without a residual image
was obtained even in a half tone display. The contrast ratio on the screen
was about 130.
The response time was 20 msec under the condition of 7 V.fwdarw.0 V, 20
msec under the condition of 0 V.fwdarw.7 V, and 100 msec under the
condition of 0 V.fwdarw.saturated transmittance.times.0.2 (about 16%).
EXAMPLE 6
Liquid crystal display elements were prepared in the substantially same as
described in Example 1 except that the physical properties and the average
particle diameter of the liquid crystal and the electrode gap in the
liquid crystal display elements for respective colors as follows. Liquid
crystal for R: .DELTA.n=about 0.29, 0.29, .DELTA..epsilon.=about 16,
K33=about 16 (.times.10.sup.-12 N), viscosity=about 54 cSt, R.sub.R =1.5
.mu.m, d.sub.R =11.0 .mu.m Liquid crystal for G: .DELTA.n=about 0.24,
.DELTA..epsilon.=about 16, K33=about 15 (.times.10.sup.-12 N),
viscosity=about 37 cSt, R.sub.G =1.5 .mu.m, d.sub.G =11.0 .mu.m. Liquid
crystal for B: .DELTA.n=about 0.24, .DELTA..epsilon.=about 16K33=about 15
(.times.10.sup.-12 N), viscosity=about 37 cSt, R.sub.G =1.5 .mu.m, d.sub.B
=10.0 .mu.m
These liquid crystal display elements were used in combination with the
projection light source and the projection optical system as shown in FIG.
1 to form a projection type liquid crystal display apparatus. The
collection cone angle was adjusted to 5.degree. and driving voltage was
adjusted to 8 V in terms of effective value. The display apparatus was
drived with a video signal to project a picture image on the screen. As a
result, a display of moving picture having good chromatic balance and
without a residual image was obtained even in a half tone display. The
contrast ratio on the screen was about 120.
The response time was 20 msec under the condition of 8 V.fwdarw.0 V, 20
msec under the condition of 0 V.fwdarw.8 V, and 100 msec under the
condition of 0 V.fwdarw.saturated transittance.times.0.2 (about 16%).
EXAMPLE 7
An active matrix liquid crystal display element was prepared in the
substantially same manner as in Example 1 except that the counter
electrode was made of aluminum to modify the display element into a
reflection type element, the substrate gap was 6.0 .mu.m and the average
particle diameter was 1.6 .mu.m. When the liquid crystal display element
was drived with a driving voltage of 5 v, it was found that T5v was 72%,
T0v was 0.6% and CR was about 120. In the liquid crystal display element
prepared, the reflectance of the surface of the element was determined to
be about 0.4%.
When the liquid crystal display element was drived with a video signal, a
display of moving picture of a half tone wherein no residual image was
produced, was obtained.
The response time was 8 msec under 5 V.fwdarw.0 V, 12 msec under 0
V.fwdarw.5 V and 100 msec under 0 V.fwdarw.saturated
transmittance.times.0.2 (about 16%).
The liquid crystal display element was combined with the projection light
source and the projection optical system to form a projection type liquid
crystal display apparatus of a reflection type. In the thus formed display
apparatus, a display of moving picture without a residual image was
obtained, and the contrast ratio on the screen was about 100.
EXAMPLE 8
Active matrix liquid crystal display elements were prepared in the same
manner as in Example 1 except that the counter electrode was of aluminum
to thereby form a reflection type element, the substrate gap was
respective d.sub.R =6.0 .mu.m, d.sub.G =5.0 .mu.m, d.sub.B =4.5 .mu.m, and
the average particle diameter were respectively R.sub.R =1.9 .mu.m,
R.sub.G =1.6 .mu.m, R.sub.B =1.5 .mu.m. The reflectance at the surface of
the liquid crystal display elements was adjusted to be about 0.3%. A
driving voltage of 5 V in terms of effective value was used. The display
apparatus was driven with a video signal to project a picture image on the
screen. As a result, a display of moving picture having good chromatic
balance and without a residual image was obtained even in a half tone
display. The contrast ratio on the screen was about 100.
The response time was 8 msec under 5 V.fwdarw.0 V, 12 msec under 0
V.fwdarw.5 V, and 80 msec under 0 V.fwdarw.saturated
transmittance.times.0.2 (about 16%).
EXAMPLE 9
An active matrix liquid crystal display element was prepared by injecting
into a cell solution obtained by dissolving uniformly acrylate monomer,
urethane acrylate oligomer, a photo-cure initiator in a nematic liquid
crystal having about 0.29 of .DELTA.n, about 16 of .DELTA..epsilon., about
15 (.times.10.sup.-12 N) of K33 and about 52 cSt of viscosity. The liquid
crystal quantity was 68 wt. %, the electrode gap was about 10 .mu.m and
the average particle diameter of the liquid crystal was about 1.4 .mu.m
respectively.
When the liquid crystal display element was drived with a driving voltage
of 8 V, it was found that T8v was 75%, T0v was 0.3% and CR was about 250
respectively.
The liquid crystal display element drived with a video signal provided a
display of moving picture of a half tone wherein no residual image was
found.
Response time (a 90% transmittance change) was 10 msec under 8 V.fwdarw.0
V, 15 msec under 0 V.fwdarw.8 V and 80 msec under 0 V.fwdarw.saturated
transmittance.times.0.2 (about 16%).
The liquid crystal display element was combined with the projection light
source and the projection optical system to thereby form a projection type
liquid crystal display apparatus having a reflection type construction.
The collection cone angle was adjusted to 6.degree.. The projection type
liquid crystal display apparatus provided a display of moving picture
without a residual image. The contrast ratio on the screen was about 120.
COMPARATIVE EXAMPLE 6
An active matrix liquid crystal display element was prepared in the same
manner as in Example 1 except that the liquid crystal used in Example 1
was replaced by a nematic liquid crystal ("E-8" manufactured by BDH)
having about 0.24 of .DELTA.n, about 16 of .DELTA..epsilon., about 18
(.times.10.sup.-12 N) of K33 and about 54 cSt of viscosity. The electrode
gap was about 11 .mu.m and the average particle diameter of the liquid
crystal was about 1.7 .mu.m.
When the liquid crystal display element was drived with 7 V, T7v was 75%,
T0v was 0.4% and CR was about 200 respectively.
The liquid crystal display element was drived with a video signal. As a
result, a display of moving picture of a half tone and little residual
image was obtained. However, a residual image was found in a dark half
tone display.
The response time (a 90% transmittance change) was 35 msec under 7
V.fwdarw.0 V, 30 msec under 0 V.fwdarw.7 V and 450 msec under 0 V
saturated transmittance.times.0.2 (about 16%).
The liquid crystal display element was combined with the projection light
source and the projection optical system to form a projection type liquid
crystal display apparatus having a reflection type structure. The
collection cone angle was adjusted to 6.degree.. In the projection type
liquid crystal display apparatus, the contrast ratio on the screen was
about 100, but a residual image was partially found.
COMPARATIVE EXAMPLE 7
Active matrix liquid crystal display elements were prepared in the same
manner as in Example 1 except that a nematic liquid crystal having about
0.24 of .DELTA.n, about 16 of .DELTA..epsilon., about 18
(.times.10.sup.-12 N) of K33 and about 54 cSt of viscosity was used.
The average particle diameter R of the liquid crystal and the substrate gap
d of the liquid crystal display elements for respective colors were
determined as follows
R: R.sub.R =2.0 .mu.m, d.sub.R =13.5 .mu.m
G: R.sub.G =1.7 .mu.m, d.sub.G =11.0 .mu.m
B: R.sub.B =1.5 .mu.m, d.sub.B =10.0 .mu.m
A driving voltage of 8 V in terms of effective value was used and the
projection type liquid crystal display apparatus was drived with a video
signal to project a picture image on the screen. As a result, a residual
image was found in a dark half tone display.
The response time was 40 msec under 8 v.fwdarw.0 V, 35 msec under 0
v.fwdarw.8 V and 400 msec under 8 V.fwdarw.saturated
transmittance.times.0.2 (about 16%) respectively.
EXAMPLE 10
An empty cell with color filters of R, G and B formed at the inner surface
was prepared. The gap of the empty cell at the red color filter portion
was d.sub.R =11.0 .mu.m; the gap at the green color filter portion was
d.sub.G =10.0 .mu.m and the gap at the blue color filter portion was
d.sub.B =9.5 .mu.m.
A solution obtained by uniformly dissolving acrylate monomer, urethane
acrylate oligomer and a photo-cure initiator in a nematic liquid crystal
was injected in the empty cell, and the cell was subjected to exposure to
UV rays to cure the liquid crystal polymer composite material. Thus, an
active matrix liquid crystal display element was prepared.
The physical properties of the liquid crystal used were about 0.24 of
.DELTA.n, about 16 of .DELTA..epsilon., about 15 (.times.10.sup.-12 N) of
K33 and about 37 cSt of viscosity, and the average particle diameter of
the liquid crystal was 1.5 .mu.m.
A black absorbing material was provided at the background of the liquid
crystal display element. The display element was drived with a video
signal. As a result, a colored display having fine gray scale wherein no
residual image was found, was obtained. The contrast ratio of the liquid
crystal display element was 100.
The liquid crystal display element was combined with the projection light
source and the projection optical system to form a projection type display
apparatus. By using the projection type display apparatus, a picture image
was projected on the screen. As a result, a color display having fine gray
scale wherein no residual image was found, was obtained. The contrast
ratio on the screen was about 70.
EXAMPLE 11
Active matrix liquid crystal display elements were prepared in the same
manner as Example 1 except that a nematic liquid crystal having about 0.24
of .DELTA.n, about 16 of .DELTA..epsilon., about 15 (.times.10.sup.-12 N)
of K33 and about 37 cSt of viscosity was used.
The average particle diameter R of the liquid crystal and the substrate gap
d of the active matrix liquid crystal display elements for R, G and B were
determined as follows:
R: R.sub.R =1.9 .mu.m. d.sub.R =12.0 .mu.m
G and B (in common): R.sub.G =R.sub.B =1.6 .mu.m, d.sub.G =d.sub.B =10.0
.mu.m.
A projection type liquid crystal display apparatus comprising the
above-mentioned active matrix liquid crystal display elements in which the
collection cone angle was adjusted to about 6.degree. was drived with a
video signal to project a picture image on the screen. As a result, a
picture image having slightly insufficient blue component was obtained. In
another attempt, the projection type liquid crystal display apparatus was
drived with a video signal wherein the active matrix liquid crystal
display elements for R and G was drived with a driving voltage of 7 V in
terms of effective value drived with a driving voltage of 8 V in terms of
effective value so that a picture image was projected on the screen. As a
result, a display of moving picture having good chromatic balance and
without any residual image was obtained in a half tone display. The
contrast ratio on the screen was about 100.
The response time was 10 msec under 8 V.fwdarw.0 v, 15 msec under 0
V.fwdarw.7 V (8 V for B), and 110 msec under 0 V.fwdarw.saturated
transmittance.times.0.2 (about 16%).
In the active matrix liquid crystal display element of the present
invention, since a liquid crystal polymer composite material which
electrically controls a scattering state and a transparent state is used
as a liquid crystal material and the liquid crystal polymer composite
material is held between an active matrix substrate and a counter
electrode substrate, polarization plates are unnecessary, whereby the
transmittance of light in a light-transparent time can be remarkably
improved and a bright picture image is obtainable by projection.
The liquid crystal display element of the present invention exhibits high
scattering property under the condition that no electric field is applied
and high transparent property under the condition that an electric field
is applied by means of the active element. Accordingly, it has a high
contrast ratio and a display of high brightness is possible even when a
conventional driving IC for a TN type liquid crystal display element is
used.
Further, in the present invention, since the characteristics of the liquid
crystal display element are optimized for color sources which provide
different kinds of color, a display having good chromatic balance can be
obtained even in a half tone. Further, even in gray scale driving,
occurrence of a residual image can be suppressed.
Accordingly, the liquid crystal display element of the present invention is
effective to a projection type display, and a projection type display
having brightness, good chromatic balance and good contrast ratio can be
obtained. Further, it is possible to reduce the size of a light source.
Further, since it is unnecessary to use the polarization plates, the
wavelength dependency of the optical characteristics is small and there is
little requirement for color correction for the light source.
Further, possible problems of orientation processing such as rubbing
necessary for the TN type liquid crystal display element and destruction
of the active element due to the orientation processing and static
electricity generated from the processing can be avoided, and the yield of
production of the liquid crystal display elements can be improved
significantly.
Since the liquid crystal polymer composite material is formed in a form of
film after curing, such problems short-circuiting between the substrate by
a pressure applied thereon and destruction of the active elements by
displacement of spacers can be minimized.
Further, the liquid crystal polymer composite material is similar in
specific resistance to that in the conventional TN mode, and great storage
capacitor need not be provided for each picture elements as in the DS
mode. Accordingly, designing of the active elements can be facilitated and
the ratio of an effective picture element electrode area can be increased,
and power consumption of the liquid crystal display element can be small.
Further, since the liquid crystal display element can be produced only by
eliminating the orientation film forming step from a conventional process
of production of the liquid crystal element of the TN mode, production of
the element can be easy.
The liquid crystal display element which employs the liquid crystal polymer
composite material has a feature that the response time is short, and a
display of moving picture can be made easily. Further, since the
electric-optical characteristics (voltage-transmittance dependence) of the
liquid crystal display element is looser than a conventional liquid
crystal display element of the TN mode, it can be easily applied to
display gray scale.
In addition, since the liquid crystal display element of the present
invention is rendered to be in transparent state upon application of an
electric field, light is scattered by a portion to which no electric field
is applied and there is no leak of light upon projection of light even if
a light shielding layer for interrupting light is not provided at the
portion other than picture elements. Accordingly, there is no necessity of
provision of a light shielding means between adjacent picture elements.
Accordingly, where an active element made of polysilicon is used, a
projection light source of a high brightness can be used without using a
light shielding layer or with a thin light shielding layer to the active
element, whereby a projection type liquid crystal display apparatus of a
high brightness can be easily obtained. Further, no light shielding layer
is necessary in this instance, and accordingly, the process of production
can be simplified.
In the present invention, various applications are possible as far as the
effect by the present invention is not injured.
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